The sampling and testing of biological fluids such as urine for the presence of analytes provide important information regarding various health-related matters, including pregnancy and conception.
In recent years, test devices have undergone nearly continuous refinement in an effort to simplify and speed the process of detecting selected ligand in fluids. As a result of this work, current test devices use an immunoassay for determining pregnancy or conception. In these devices a reagent, such as an antibody, specifically reacts with an analyte to form a complex, which can usually be detected by the unaided eye.
Current pregnancy test devices assay for hormones associated with pregnancy, such as, for example, chorionic gonadotrophin (hereinafter "hCG") since the presence of hCG in urine is usually an indicator that a woman is pregnant. Such test devices obtain qualitative results indicating either the presence or absence of hCG. Typically, a pregnancy immunoassay contains an antibody directed against hCG. The reaction complex can then be viewed by the user.
Conception test devices also assay for hormones associated with the ovarian cycle, such as, for example, luteinizing hormone (hereinafter "LH"). LH is present normally in urine but its concentration increases markedly during ovulation, the time at which a woman is most likely to conceive. Thus, the probability that a woman can conceive a child varies directly with LH concentration. Such test devices obtain semi-quantitative results regarding the relative concentration of LH in the urine. Typically, a conception immunoassay contains an antibody directed against LH and a separate detection antibody.
In known devices, the fluid to be tested wicks up through an absorbent membrane that is in fluid flow contact with the reagents that detect an analyte in a fluid. A major problem with this type of device is that as the fluid progresses through the membrane, the front edge of the fluid is uneven. The uneven fluid front will cause the results to be smeared, produce false negatives and make the results difficult to detect. These artifacts are called "leading edge effects." An uneven fluid front can arise for a variety of reasons, for example, because the sample is not uniformly applied to the absorbent membrane.
Therefore, a need exists for a device that does not produce an uneven fluid front and associated leading edge effects. The present invention provides a device that eliminates the uneven fluid front problem and related methods of using such a device.